poopy bottom and egg concerns

One of our BR's continually has a poopy bottom and always lays eggs that have calcium "bumps" all over them. She has laid a few soft eggs (maybe 4 and not all in a row). Her shells are thin compared to the other girls and she herself is larger than the other girls. They all have access to fresh water, layer feed, oyster shells and grit. They free range during the day. I read threads on how to clean her bottom and I am going to do that in the morning. She's the sweetest of the bunch but mother's instinct tells me somethings not quite right. Any thoughts? (no one else is having poopy bottom and soft eggs)

You gotta love that face!